The present invention relates to a protection system of a turbomachine; and more particularly to a method and system for electronic overspeed protection on a turbomachine.
An overspeed condition occurs after the speed of a shaft on a turbomachine exceeds a specified range. During the overspeed condition, a turbomachine typically experiences severe mechanical and thermal stresses that can cause a catastrophic failure. An overspeed protection system protects the turbomachine by initiating an emergency shutdown (commonly called a trip) during an overspeed event.
Prior to testing the overspeed protection system, the turbomachine is customarily operating in a full-speed-no-load (FSNL) condition. FSNL is a condition where the turbomachine is at a normal operating speed and not exporting energy to a load such as a generator, compressor, or the like. An overspeed test typically involves manually raising the speed of a turbomachine above the normal operating range. For example, during an overspeed test some turbomachine operators raise the speed to 110% of the normal operating speed; thereafter the overspeed protection system should trip the turbine.
There are a few problems with the current method of overspeed testing. Manually adjusting the shaft speed introduces high thermal transients. A turbomachine trip at a speed near or above the normal operating speed can introduce large mechanical, electrical, and thermal stresses on the turbomachine components. These stresses decrease the maintenance interval and require turbomachine operators to shutdown the turbomachine for maintenance at a time sooner than planned. Moreover, after a trip, a re-start of a turbomachine is required, which delays the exporting of energy. Also, the current overspeed testing methods typically require that the turbomachine operate at FSNL, which typically does not generating revenue but consumes fuel and electricity. These problems drive turbomachine operators to avoid manual speed adjustments, trips, FSNL operation, and overspeed testing.
For the foregoing reasons, there is a need for a method and system for testing an overspeed protection system that does not trip the turbomachine at an operating speed that will introduce high thermal transients. The method should automatically adjust the speed during testing and should not require a turbomachine re-start after testing. Furthermore, the method should not require significant FSNL operation.